Whenever approaching difficult rhythms, I always recommend subdividing into smaller values. For this example, we can subdivide this into eighth notes.
Assuming this is in 4/4 time, we have eight eighth notes in the measure, often counted "1 & 2 & 3 & 4 &."
The first eighth note only takes up one of these eighth notes, the "1."
The next note, a dotted quarter, takes up three eighth notes. This is because the dot adds half the value of what precedes it. Since a quarter takes up two eighth notes, this dot add half of that two. Two and one make three, so this note is worth three eighth notes.
But it's also tied to another dotted quarter, so we have a value of three eighth notes tied to another three, so these two notes take up sixth eighth notes altogether.
Since the first note only took up the first "1," this next articulation begins on the "&" immediately after and takes us through '2 & 3 & 4.'
The final note is of course just a single eighth note, so it takes the final "&" of the measure.
So to count this, I recommend starting by saying, out loud, "1 & 2 & 3 & 4 &."
Then, remove the non-articulated eighth notes: 1 & (2 & 3 & 4) &.